In pressure wave superchargers for supercharging internal combustion engines of vehicles, control of the supercharge air pressure is often necessary because of the wide range of engine rotational speeds. Providing the pressure wave supercharger with an exhaust gas by-pass having a shut-off device controlled by a medium may advantageously provide such control. The pressure wave supercharger is, in this case, so designed that the theoretically attainable supercharge pressure, in the absence of exhaust gas blow-down, is greater than the allowable supercharge pressure limit which the engine can withstand at the upper engine rotational speeds. In order, however, to remain below the allowable supercharge pressure limit, part of the exhaust gases must be blown down beyond a certain engine rotational speed. This type of control has a positive effect on the variation of available engine torque and fuel consumption, particularly in the case of engines which are not mainly operated at higher rotational speeds.
A control device for controlling the supercharge pressure by appropriate blow-down of the engine exhaust gases in a pressure wave supercharger, mentioned initially, includes the applicant's own contribution to the state of the art. In this solution, the shut-off device is directly actuated by the gas pressure or any other process pressure. However, the high supercharge pressure reserves of the pressure wave supercharger in the middle rotational speed range cannot be utilised because blowdown of the exhaust gas starts too early, i.e. before the allowable supercharge pressure limit is reached, because of the inertia and an unfavourable opening characteristic of the shut-off device.